Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item The evolution of the chemical abundance gradients in the merging Magellanic Cloud dwarf galaxies(Montana State University - Bozeman, College of Letters & Science, 2023) Povick, Joshua Tyler; Chairperson, Graduate Committee: David L. Nidever; This is a manuscript style paper that includes co-authored chapters.Dwarf galaxies are some of the most abundant objects in the Universe, but most of them are very distant and very faint. While observing these galaxies does pose some challenges, they are important to study because it is believed that larger galaxies, such as the Milky Way (MW), form from a series of dwarf mergers in a process called hierarchical merging. As if by chance, the Magellanic Clouds (MCs) are both bright enough and close enough to resolve individual stars. These two dwarf satellites of the MW are also in the process of merging together, presenting a great opportunity to examine how the abundance gradients of galaxies are impacted by intergalactic interactions. A great tool to study the MCs is the Apache Point Galactic Evolution Experiment (APOGEE). APOGEE is an H-band near infrared survey commissioned to measure chemical abundances and accurate radial velocities of the MW and its neighborhood. In the MCs, APOGEE was able to observe 6130 red giant branch (RGB) stars in the Large Magellanic Cloud (LMC) and 2062 RGB stars in the Small Magellanic Cloud (SMC). Individual stellar ages are derived using multiband photometry and spectroscopic parameters to compare to stellar isochrones. Using the abundance measurements of 20+ elements and the derived stellar ages, abundance gradients and their evolutions are extracted from radial abundance trends. The stellar ages in the LMC reveal that recent star formation has been concentrated in the center of that galaxy. The fields that overlay a spiral arm in the north of the LMC reveal median ages of ?2 Gyr. The age-metallicity relation (AMR) remains mostly flat with the exception of an increase in overall metallicity ?2 Gyr ago. Looking at the evolution of many abundance gradients in the LMC there is a U-shaped trend with an extremum around the same time as the increase in metallicity. Additionally, the SMC also shows a U-shaped trend in its abundance gradient evolutions albeit a few billion years earlier than the LMC. These results all correspond to a conjectured close interaction between the LMC and SMC in the recent past.Item Exploring the origin of the Magellanic periphery with SMASH photometric metallicities(Montana State University - Bozeman, College of Letters & Science, 2019) Miller, Amy Elizabeth; Chairperson, Graduate Committee: David L. NideverThe distribution of stellar metallicities across the Large and Small Magellanic Clouds is a key ingredient to understanding the processes that have shaped their evolution, and remains a rich ground for exploration. I use data from the Survey of Magellanic Stellar History (SMASH), a photometric survey of the Magellanic Clouds that contains approximately 400 million objects in 197 fields that were obtained with DECam on the CTIO Blanco 4m telescope. SMASH covers 2400 square degrees to 24th magnitude in ugriz, encompassing a depth of 2 magnitudes below the oldest main-sequence turnoff stars. The DECam u-band is sensitive to metallicity for main-sequence turn-off stars, which is calibrated using SDSS and LAMOST spectroscopy in overlapping regions. This analysis is used to make accurate metallicity maps of the main bodies of the Clouds and their peripheries. Ultimately, these metallicity maps will help us trace out population gradients in the Clouds and uncover the origin of their very extended stellar peripheries.Item Superfluid effects on thermal evolution and rotational dynamics of neutron stars(Montana State University - Bozeman, College of Letters & Science, 2001) Larson, Michelle Beauvais